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Harhun M.I.,St Georges, University of London | Harhun M.I.,Bogomoletz Institute of Physiology
Cell Calcium | Year: 2015

Vasomotion is the rhythmical changes in vascular tone of various blood vessels. It was proposed that in rabbit portal vein (RPV) the spontaneous contractile activity is driven by vascular interstitial cells (VICs), since RPV VICs generate rhythmical changes in intracellular Ca2+ concentration ([Ca2+]i) associated with membrane depolarisation in these cells. In this work, using confocal imaging in Fluo-3 loaded RPV VICs we studied if generation of rhythmical [Ca2+]i changes is affected when Ca2+ handling by mitochondria is compromised. We also visualised mitochondria in VICs using Mito Tracker Green fluorescent dye.Our results showed that freshly dispersed RPV VICs generated rhythmical [Ca2+]i oscillations with a frequency of 0.2-0.01Hz. Imaging of VICs stained with Mito Tracker Green revealed abundant mitochondria in these cells with a higher density of the organelles in sub-plasmalemmar region compared to the central region of the cell. Oligomycin, an ATP synthase inhibitor, did not affect the amplitude and frequency of rhythmical [Ca2+]i oscillations. In contrast, two uncoupling agents, carbonylcyanide-3-chlorophenylhydrazone (CCCP) and carbonylcyanide-4-trifluoromethoxyphenylhydrazone (FCCP) effectively abolished rhythmical [Ca2+]i changes with simultaneous increase in basal [Ca2+]i in RPV VICs.These data suggest that in RPV VICs mitochondrial Ca2+ handling is important for the generation of rhythmical [Ca2+]i changes which underlie the spontaneous rhythmical contractile activity in this vessel. © 2015 Elsevier Ltd.

Stepanyuk A.,Bogomoletz Institute of Physiology
Biologically Inspired Cognitive Architectures | Year: 2015

The grid cells (GCs) of the medial entorhinal cortex (MEC) and place cells (PCs) of the hippocampus are assumed to be the key elements of the brain network for the metric representation of space. Existing theoretical models of GC network rely on specific hypotheses about the network connectivity patterns. How these patterns could be formed during the network development is not fully understood. It was previously suggested, within the feedforward network models, that activity of PCs could provide the basis for development of GC-like activity patterns. Supporting this hypothesis is the finding that PC activity remains spatially stable after disruption of the GC firing patterns and that the grid fields almost disappear when hippocampal cells are deactivated. Here a new theoretical model of this type is proposed, allowing for grid fields formation due to synaptic plasticity in synapses connecting PCs in hippocampus with neurons in MEC. Learning of the hexagonally symmetric fields in this model occurs due to complex action of several simple biologically motivated synaptic plasticity rules. These rules include associative synaptic plasticity rules similar to BCM rule, and homeostatic plasticity rules that constrain synaptic weights. In contrast to previously described models, a short-term navigational experience in a novel environment is sufficient for the network to learn GC activity patterns. We suggest that learning on the basis of simple and biologically plausible associative synaptic plasticity rules could contribute to the formation of grid fields in early development and to maintenance of normal GCs activity patterns in the familiar environments. © 2015 Elsevier B.V. All rights reserved.

Isaeva E.,Neuroscience Center at Dartmouth | Isaeva E.,Bogomoletz Institute of Physiology | Hernan A.,Neuroscience Center at Dartmouth | Isaev D.,Neuroscience Center at Dartmouth | And 2 more authors.
Annals of Neurology | Year: 2012

Objective: An epileptic seizure is frequently the presenting sign of intracerebral hemorrhage (ICH) caused by stroke, head trauma, hypertension, and a wide spectrum of disorders. However, the cellular mechanisms responsible for occurrence of seizures during ICH have not been established. During intracerebral bleeding, blood constituents enter the neuronal tissue and produce both an acute and a delayed effect on brain functioning. Among the blood components, only thrombin has been shown to evoke seizures immediately after entering brain tissue. In the present study, we tested the hypothesis that thrombin increases neuronal excitability in the immature brain through alteration of voltage-gated sodium channels. Methods: The thrombin effect on neuronal excitability and voltage-gated sodium channels was assessed using extracellular and intracellular recording techniques in the hippocampal slice preparation of immature rats. Results: We show that thrombin increased neuronal excitability in the immature hippocampus in an N-methyl-D-aspartate-independent manner. Application of thrombin did not alter transient voltage-gated sodium channels and action potential threshold. However, thrombin significantly depolarized the membrane potential and produced a hyperpolarizing shift of tetrodotoxin-sensitive persistent voltage-gated sodium channel activation. This effect of thrombin was attenuated by application of protease-activated receptor-1 and protein kinase C antagonists. Interpretation: Our data indicate that thrombin amplifies the persistent voltage-gated sodium current affecting resting membrane potential and seizure threshold at the network level. Our results provide a novel explanation as to how ICH in newborns results in seizures, which may provide avenues for therapeutic intervention in the prevention of post-ICH seizures. Copyright © 2012 American Neurological Association.

Harhun M.I.,St Georges, University of London | Povstyan O.V.,St Georges, University of London | Povstyan O.V.,Bogomoletz Institute of Physiology | Albert A.P.,St Georges, University of London | Nichols C.M.,St Georges, University of London
Stroke | Year: 2014

BACKGROUND AND PURPOSE - : Current knowledge states that vasoconstrictor responses to ATP are mediated by rapidly desensitizing ligand-gated P2X1 receptors in vascular smooth muscle cells (VSMCs). However, ATP is implicated in contributing to pathological conditions involving sustained vasoconstrictor response such as cerebral vasospasm. The purpose of this study is to test the hypothesis that the stimulation of VSMC P2XR receptors (P2XRs) contributes to ATP-evoked sustained vasoconstrictions in rat middle cerebral arteries (RMCAs). METHODS - : Reverse transcription- polymerase chain reaction, Western blot, and immunocytochemistry were used to analyze expression of mRNA and proteins in RMCAs VSMCs. Ionic currents and calcium responses were investigated using patch-clamp and confocal imaging techniques, respectively. Functional responses were confirmed using wire myography. RESULTS - : Expression of mRNA and protein for P2X1R and P2X4R subunits was identified in RMCA VSMCs. Confocal imaging in fluo-3-loaded VSMCs showed that ATP and a selective P2XR agonist, αβmeATP, evoked similar dose-dependent increases in [Ca]i. Patch-clamp experiments identified 2 components of P2XR-mediated currents: consisting of a fast desensitizing phase mediated by homomeric P2X1Rs and a slowly desensitizing phase involving heteromeric P2X1/4Rs. Isometric tension measurements showed that 80%:20% of initial ATP-evoked vasoconstriction in RMCA is mediated by homomeric P2X1Rs and heteromeric P2X1/4Rs, respectively. The sustained slowly desensitizing and rapidly recovering from desensitization responses are mediated by heteromeric P2X1/4Rs. CONCLUSIONS - : This study reveals for the first time that apart from rapidly desensitizing homomeric P2X1Rs, heteromeric P2X1/4Rs contribute to the sustained component of the purinergic-mediated vasoconstriction in RMCA. Our study, therefore, identifies possible novel targets for therapeutical intervention in cerebral circulation. © 2014 American Heart Association, Inc.

Skibo G.G.,Bogomoletz Institute of Physiology
Vitamins and hormones | Year: 2010

Brain plasticity describes the potential of the organ for adaptive changes involved in various phenomena in health and disease. A substantial amount of experimental evidence, received in animal and cell models, shows that a cascade of plastic changes at the molecular, cellular, and tissue levels, is initiated in different regions of the postischemic brain. Underlying mechanisms include neurochemical alterations, functional changes in excitatory and inhibitory synapses, axonal and dendritic sprouting, and reorganization of sensory and motor central maps. Multiple lines of evidence indicate numerous points in which the process of postischemic recovery may be influenced with the aim to restore the full capacity of the brain tissue injured by an ischemic episode. Copyright 2010 Elsevier Inc. All rights reserved.

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